Field of the Invention
The invention relates to rotors or rotor cores for electrical motors. Specifically, the invention relates to the geometry of rotor core assemblies and their placement or attachment at the shaft of an electrical motor.
Brief Description of the Related Art
Rotors of electrical motors usually have a rotor core assembly that is attached to the shaft of the electrical motor rotating-resistantly and permanently. In addition to other attachment methods, the rotor core is frequently attached to the shaft with a press fit.
The rotor core as such, which comprises permanent or electromagnets and possibly the corresponding coils, frequently comprises of a package of sheets that are pressed or glued to each other. The individual sheets are usually produced by punching and subsequently aligned with each other and packetized.
For durability and reliability of the electrical motors, it is essential that the rotor core is attached to the shaft permanently and fixedly. In addition to procedurally elaborate bonding or other attachment methods, pressing is frequently used for manufacture-technical reasons and the rotor core is thus attached to the shaft by press fit.
To improve the fit of the rotor core assembly on the shaft, it is known from U.S. Pat. No. 6,720,702 to provide a groove in the shaft and the rotor core assembly into which a guide element is inserted. This warrants rotationally safe attachment, which, however, requires an additional production step. In addition to this, use of the attachment pin in one side of the shaft causes an imbalance when turning the electrical motor.
From U.S. Pat. No. 6,069,432, it is known to provide for a sleeve between the rotor core and the shaft that warrants secure fit of the rotor core on the shaft. The sleeve has an inner diameter that essentially corresponds to the outer diameter of the shaft and an outer diameter that essentially corresponds to the inner diameter of the rotor core. Additionally, the cross-section of the sleeve is not perfectly circular at its inner diameter but has several narrower points that ensure a tight press fit when pushing the sleeve onto the shaft. The deformation of the sleeve when attaching it to the shaft deforms it to achieve tight fit on the rotor core assembly. This procedure is rather elaborate and requires use of a special sleeve.